Abstract Infrared Absorption measurements of oxygen in silicon and germanium were made with IE Fourier Transform Spectrometer at temperatures between 6 K and 300 K in the region of 400-4000cm-1. Resolution was up to 0.5cm-1 when high resolution conditions were adopted.Detection limit and sources of error on oxygen concentration of silicon and germanium determined by infrared absorption measurement at low temperature were identified. Using a 2 cm thick sample, the- lower limit of detectability for oxygen at 20 K is estimated to be 9.6×1014 oxygen atom. cm-3 and 3.0×1014 oxygen atom. cm-3 in silicon and germanium respectively. The oxygen concentration of CZ germanium single crystals with different growth conditions was also studied and these results determined by IE measurements havebeen investigated and discussed at temper-lithium precipitation technique.Temperature-dependent fine structure of 1106 cm-3 absorption band of silicon with different oxygen concentration have been investigated and discussed at temper atures between 6 K and 300 K.